CH627705A5 - METHOD FOR SEALING A PLASTIC LID ON A CONTAINER, AND DEVICE FOR CARRYING OUT THE METHOD. - Google Patents

Description

The invention relates to a method for sealing a plastic lid onto a container made of plastic-coated cardboard according to the preamble of patent claim 1, and to a device for carrying out the method according to the preamble of patent claim 8.

In a known method for sealing a lid onto the top of a container, heat is supplied to the lid and thus to the container via heated jaws pressed against the lid. In this case, the heat is supplied to the lid and to the container by means of heat transfer from the outwardly facing support surfaces into the lid and the container. As a result, the temperature on the outer surfaces must be higher than the temperature inside the material to be heated; furthermore, rapid heating requires a very high jaw temperature.

In current production, such heat supply by heat convection via heated jaws is not very advantageous for sealing a plastic lid onto a container made of plastic-coated cardboard, because the supply of the necessary energy takes too long a time until the jaw temperature is high enough. This also results in such a high jaw temperature that a plastic lid produced by vacuum molding will deform and shrink.

The object of the invention is to provide a method and a device for sealing a plastic lid on a container made of plastic-coated cardboard, in which the aforementioned disadvantages can be avoided.

The method according to the invention is characterized in that the closed container is supplied with energy in the form of electromagnetic microwaves at several points on the contact surface between the lid and the container, so that this energy is absorbed by the carton, which heats up to a temperature,

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which causes the coating of the cardboard to melt in order to weld the lid in the form of a spot weld on the cardboard.

Advantageously, the locations to which microwave energy is supplied can be exposed to mechanical pressure, by means of which the melted layer areas of the cardboard are held in firm contact with the lid.

In practice, such a process can be carried out without deformation of the plastic container due to the heat developed, since the absorption of the microwave energy in the plastic material compared to the absorption of such energy in the cardboard and paper, provided that these materials have a suitable moisture content, is relatively small.

If the lid already exerts a certain pressure on the upper edges of the container, there is no longer any need for an additional mechanical pressure load at the sealing zone during the sealing, because the conversion of the microwave energy into heat in the carton without mechanical contact between the microwave source and the one with heat to be supplied and sealed parts. However, in the case of special types of lids, it can be advantageous to apply a mechanical pressure to the sealing points, preferably simultaneously with the supply of the microwave energy. If desired, mechanical pressure can also be brought about after the microwave energy has been supplied.

The lid is not sealed more tightly than necessary to allow the lid to be opened later by the user. In addition to forming attachment points between the lid and the container, the sealing points also serve as a check that the container has been opened.

To ensure that the lid is in the correct position before it is sealed onto the container, a vertically directed pressure can be applied to the lid before or at the same time as microwave energy is supplied to bring the container into its final position.

The device for performing the method according to the invention is characterized according to the features of claim 8. In a preferred embodiment of this device, the arms are attached to the walls of a chamber in which the upper part of the sealed container is located. Metal rails hang from the inside of the walls and are arranged within the microwave supply means at a distance from them which corresponds approximately to the width of the U-shaped groove running along the circumference of the cover.

An embodiment of a device according to the invention is explained below with reference to drawings. Show it:

1 is a schematic vertical section through an embodiment of a device with the features according to the invention,

Fig. 2 is a sectional view of a section along the line II-II in Fig. 1, in which some parts are shown half broken away.

According to the drawing, an upper container part 1 of a container made of plastic-coated cardboard has an approximately square cross section. A plastic cover 2 is placed on the top of the container 1 and has a U-shaped groove 3 along its circumference with an outer and an inner flange 5a, 5, which surrounds the upper edge 4 of the container. The inner flange 5

passes over a horizontally directed narrow region 6 into a raised central section 7.

In the drawing, a so-called microwave heating inductor 8 is provided above and around the lid 2 of the container 5, which is equipped with a control device, not shown, which gives the heating inductor 8 a vertical movement up and down. In its lower position shown in Fig. 1, the heating inductor 8 surrounds the upper part of the covered container 1, meanwhile in an upper, not shown, second position it is raised enough to be removed from the container and its removal from the area to allow below the heating inductor.

The heating inductor 8, which is shown very schematically in the drawing, mainly consists of a chamber 9 with an upper section 10, which has a larger cross-sectional area than the container. This upper section has bent side sections 11 which merge into essentially vertical end edges 12, the shape and size of which was selected such that they enclose the upper part of the container 1 with a comparatively small play 13, which is, however, large enough, to be able to insert the top of the container 1 into the chamber 9 25.

At the top of chamber 9, i.e. A line connection 14 is screwed onto the upper section 10 and has an external thread 15 for connecting a magnetron (not shown). A magnetron is known to consist of an anode and a cathode, which are supplied with different DC potential during operation and has a special shape which causes the transmission of electrons between the cathode and the anode to induce microwave vibrations, which are one of the Magnetron structure have the corresponding frequency. The microwaves generated by the magnetron, e.g. have a frequency of 2450 MHz are passed through an antenna. Such an antenna or a waveguide is shown in the drawing as a cylindrical rod 16 which extends centrally through the line connection 14 and is connected at its lower end to a four-armed cross 17. At the free end of each arm 17a-17d of the cross 17, a cross bar 18 is carried, which at its ends merges into a combined 45 holding and waveguide rail 19. Thus, eight similar waveguide rails 19 are provided in the exemplary embodiment shown, each of which is attached with its upper end to the inner walls of the chamber 9 and which in the region below the crossbars 18 leads to an inwardly curved section 20 in the direction of the cover 2 of the container are bent. The rod 16, the cross 17, the transverse rods 18 and the curved sections 20 of the rails 19 together form a wave guide compound for the electromagnetic waves which are generated in the magnetron described above. The electromagnetic waves split up and follow the connected waveguides until they are transmitted at the curved ends 21 of the curved sections 20 through the lid 2 and the container.

60 Since the absorption of microwave energy in plastic material is relatively low compared to the absorption of such energy in cardboard or paper, most of the energy emitted by the waveguides 21 is absorbed by the cardboard of the container 1, so that in addition to the Ends 21 heat is developed. This heat development leads to a sufficiently high temperature on the outer surface of the container, i.e. on the opposite to the outer flange 5a of the cover

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the area to melt the plastic layer on the box.

When the U-shaped groove 3 of the lid 2 exerts pressure on the upper edge of the container, a seal is brought about in the heated area between the lid and the container and the microwave energy is transferred to the carton and converted into heat in the carton without that there is contact between the microwave source and the parts to be sealed. However, in connection with a special type of cover, it can be advantageous to exert a mechanical pressure on the sealing points, this pressure preferably being exerted simultaneously with the supply of microwave energy.

For this purpose, four pressure rails 22 are provided in the chamber 9, each of which extends parallel to the inner flange 5 of the cover 2 and is connected to the inner wall of the chamber 9 via support rails 23. The pressure load on the U-shaped groove 3 of the cover can be designed by a sufficiently close juxtaposition of the waveguide ends 21 and the pressure rails 22 and by a special shape of the pressure rails 22 so that they are the flanges 5 and 5a of the U-shaped groove 3 compress with sufficient force to seal when the heating inductor is lowered into its working position. Of course, it should be noted that the pressure is not too high so that the heating inductor can be removed again without difficulty after the end of the work process.

In order to ensure that the lid 2 is correctly positioned on the container, the heating inductor 8 in the embodiment shown comprises a horizontal plate 24 which extends between the pressure rails 22 and which serves to exert vertical pressure on the raised central region 7 of the container when the Heating inductor is lowered into its working position. Together with the plate 24, the lower edges of the pressure rails 22 also support the formation of the vertical pressure.

If desired, the waveguide rails 19 and the pressure rails 22 can be arranged such that they can perform either an oscillating or a translatory movement, so that mechanical pressure for compressing the U-shaped groove of the cover is preferably carried out simultaneously with or immediately following the supply of Microwave energy can be exerted.

With a movable configuration of the pressure rails 22, the pressure plate 24 must of course be attached in a different way than shown in Fig. 1, e.g. independently supported by the upper portion 10 of the chamber 9.

The described device creates a seal of the lid which is firm enough to ensure a satisfactory mechanical hold of the lid on the container, but which is not firm enough to allow the connection to be broken later by a user. In addition to forming a secure attachment of the lid on the container, the seals also serve as a means of checking non-opened containers.

In the described embodiment of the device according to the invention, the sealing takes place between the outer flange 5a of the groove 3 and the outer plastic coating of the container in very limited zones.

The seal or welding can be broken open when the user grips the flange 5a and bends or pulls it outwards.

The device can also be used for cardboard boxes which, in addition to a double plastic-coated cardboard blank, have a thin metal coating, e.g. made of aluminum. Such a film is usually applied to the inside of the container and covered with an additional plastic layer. To this extent, the io film does not impede the possibility of the carton absorbing the microwave energy which is transmitted by the wave-guiding parts of the heating inductor 8. The aluminum foil reflects the transmitted microwaves and such a reflection increases the intensity of the wave energy in the absorption area of the cardboard. It is known that aluminum is a good heat conductor, but since the cardboard is heated very quickly and since the aluminum foil radiates the heat into the plane of the cardboard, the heat developed does not develop an undesirably high temperature on the inner plastic layer.

In connection with certain types of containers for single use, it can be advantageous to increase the number and size of the sealing zones, if desired also the pressure rails 22, even if they have a modified design, can act as microwave lines. In connection with types of lids, as shown in the drawing, an inner sealing zone is then also obtained along the U-shaped groove of the lid, an effect which in most cases requires the lid to be broken open or detached to open the container .

The method and the device according to the invention are particularly suitable for plastic-coated cardboard containers which carry plastic lids produced by vacuum molding, and the energy directed to the sealing zones does not cause the lids to deform or shrink. Of course, the invention can also be used in the case of plastic covers which have been produced by other processes, if it is ensured that the outer coating of the cover and the outer position of the container have properties such that they do not stick together in a sufficiently heated state.

It can be seen that the method and the heating inductor for producing a seal of a plastic cover on a plastic-coated cardboard container can also be used for a liquid-tight sealing of the lid with the container. The individual waveguides would then have to take on a special shape, which means that so much microwave energy is supplied along the U-shaped groove in the cover that a band made of a material that has a viscous, sticky consistency is put into the groove beforehand is made sufficiently easy to flow so that it melts at the top edges of the container. After the microwave energy supply has ended, not only a point seal along the groove is obtained on cooling, but also a liquid-tight seal. The liquid-tight seal is created because the chosen sealing material is a material that has a viscous consistency at normal room or storage temperature, which gets a lower viscosity when heated. The material has a dielectric constant that is slightly larger than that of plastics.

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Claims (12)

627 765 2nd PATENT CLAIMS 1. A method for sealing a plastic lid (2) onto a container (1) made of plastic-coated cardboard, the lid being pressed down over the upper edge of the container (4) and the lid (2) having a U-shape along its Is provided circumferential region and open in the downward groove (3), which serves to receive the upper container edge (4), characterized in that the closed container (1, 2) at several points of the contact surface between the lid and the container energy in the form Electromagnetic microwaves is supplied and that this energy is absorbed by the carton, which heats up to a temperature which causes the coating of the carton to melt to weld the lid onto the carton. 2. The method according to claim 1, characterized in that a tape made of a material which has a viscous, sticky consistency at normal room temperature and becomes easily flowing when heated to a temperature above normal room temperature, before putting on the lid (2) on the upper edge of the container (4) is inserted into the U-shaped groove (3), and that along the U-shaped groove in the lid (2) so much energy is supplied in the form of electromagnetic micro-waves that the material of the above-mentioned tape is made easy-flowing and is melted on the upper edges of the container in order to weld the lid and carton in a liquid-tight manner. 3. The method according to claim 1, characterized in that the locations which are supplied with microwave energy at the first moment are exposed to a mechanical pressure which keeps the molten layer regions of the cardboard in firm contact with the lid (2). 4. The method according to claim 3, characterized in that the mechanical pressure is effected simultaneously with the supply of microwave energy. 5. The method according to claim 3, characterized in that the mechanical pressure is effected following the supply of microwave energy. 6. The method according to claim 1, characterized in that immediately before or simultaneously with the supply of microwave energy, a vertically directed pressure is exerted on the cover (2) in order to bring it into its correct position. 7. The method according to claim 1, characterized in that microwave energy is supplied to the top of the container provided with the lid from the inner and outer side of the container, around an inner and a along the U-shaped groove (3) of the lid (2) to maintain the outer sealing zone. 8. An apparatus for performing the method according to claim 1, comprising an energy source, a microwave generator and a heating inductor (8) with waveguides (18-20), characterized in that the waveguides (18-20) of the heating inductor (8) four cross-shaped to each other have standing arms (17a-17d) of approximately the same length, which extend over the circumference of the cover (2), so that the waveguides (18-20) are supplied with the microwave energy from the generator via the four arms (17a-17d) that the heating inductor (8) is provided with a control device for raising and lowering the waveguides (18-20) in the region of the container provided with the lid (2), and that the arms (17a-17d) are provided with a free end or several means (21, 20) are provided, which lie in the lowered position of the waveguides close to the side edge of the lid and for guiding the microwave energy from the arms (17a-17d) through the lid (2) to the container (1) serve en. 9. The device according to claim 8, characterized in that the arms (17a-17d) are attached to the walls of a chamber (9) in which the upper part of the container (1) provided with the lid (2) is located , and that in the chamber (9) the microwave feed means (20, 21) oppositely arranged pressure rails (22) are provided which are at a distance from said means (20, 21) that is approximately the width of the circumference of the lid (2) extending U-shaped groove (3) corresponds. 10. The device according to claim 8, characterized in that the microwave supply means (20, 21) and / or the pressure rails (22) for effecting a mechanical pressure simultaneously with or following the supply of microwave energy to compress the U-shaped groove (3 ) of the cover (2) are movably attached. 11. The device according to claim 9, characterized in that the pressure rails (22) for pushing down the lid (2) on the top of the container serve to close the lid (2) shortly before or simultaneously with the action of the microwave supply means (20, 21) to put it in the correct position. 12. The device according to claim 9, characterized in that the microwave supply means (20, 21) opposite pressure rails (22) are designed to conduct microwave energy, wherein the pressure rails (22) are made of metal.